A fuel cell is an energy conversion device that consists essentially of two opposing electrodes, an anode and a cathode, ionically connected together via an interposing electrolyte. Unlike a battery, fuel cell reactants are supplied from an external reactant supply source. Fuel cells operate by converting a reactant fuel such as hydrogen or a hydrocarbon (e.g., methanol) to electrical power through an electrochemical process rather than by combustion. It does so by harnessing the electrons released from controlled oxidation-reduction reactions occurring on the surface of a catalyst. A fuel cell can produce electricity continuously so long as proper reactants (i.e., a fuel and an oxidant) are supplied from an outside source.
Most conventional micro-scale fuel cell systems include a stack of electrically interconnected electrode pair assemblies (commonly referred to as a fuel cell stack assembly), wherein each electrode pair is configured to receive and react with selected reactants (e.g., methanol and air flowstreams delivered across respective outer electrode surfaces). The interposing electrolyte of most conventional micro-scale liquid-air fuel cell systems (e.g., direct methanol fuel cell (DMFC) systems) generally consist of a solid polymer proton exchange membrane (PEM) (e.g., NAFION). These known micro-scale fuel cell systems all comprise an interconnected series of electrode pair assemblies, wherein each electrode pair utilizes a solid polymer proton exchange membrane as a separator and as a proton (H+) transfer medium.
In contrast, certain liquid-liquid fuel cell systems do not utilize a central PEM. In general, liquid-liquid fuel cell systems typically comprise electrode pairs and related stack assemblies that include a series of micro fluidic flow channels for flowing liquid reactant/electrolyte flowstreams (i.e., electrolytic fuel and oxidant flowstreams referred to herein as anolyte and catholyte flowstreams, respectively) adjacent to and/or through discrete regions of accompanying porous electrode structures.